Actually, it can get cold. The winter temperatures in the North fall the lowest in December and January. In the Northern mountainous regions such as Sa Pa, Moc Chau, Son La, Tam Dao and Hoang Lien Son, the temperature can sometimes get down to 0°C with snow.

During the days, in the areas where it is very cold, you will be more than likely be trekking or walking, so the cold is not too much of a problem, and actually pleasant. It is at night, when the sun goes down, that you will appreciate the warm sweater and long underwear that you brought with you. Remember to try and leave you cotton clothes at home during this time.

All of the other places in Vietnam (Hanoi, Halong Bay, Danang, Saigon) have very mild weather in the winter. With clear days and cool nights, travel in Vietnam is pleasant and weather is rarely an issue.

Tip: Most hotel air conditioners are also heaters if you need a little extra heat. 

See also other FAQs

What is the best type of clothing we should bring?

Will it be hot and humid in most places?

How hot is that in the summer?

What is it this like to travel in monsoon season; will it cause trouble for us?